We propose and experimentally demonstrate a high efficient circularly polarizing dichroism waveplate (CPDW) using a Si-based all-dielectric 2Dchiral metasurface. We demonstrate that the CPDW exhibits a unique dichroism in that it functions as a transmissive quarter waveplate for one of either left-or right-handed circularly polarized incident lightand a reflective mirror for the opposite polarization. The circular polarization dichroism (CPD = IRCP − ILCP) in transmission at wavelength ~1.5 μm reaches 97% and the extinction ratio (ER = IRCP/ILCP) is as high as 345:1. Experimental fabrications and measurements of the proposed all-dielectric metasurface are implemented and found to be in excellent agreement with the simulations. The proposed all-dielectric chiral metasurface is of advantages of high-dichroism, easy-fabrication and standard semiconductor fabrication techniques compatible, which could lead to enhanced security in fiber and free-space communications, as well as imaging and sensing applications for circularly polarized light with a highly integrated photonic platform.

We propose and experimentally demonstrate a broadband and high efficient circularly polarizing dichroism using a simple single-cycle and single-helical plasmonic surface array arranged in square lattice. Two types of helical surface structures (partially or completely covered with a gold film) are investigated. It is shown that the circular polarization dichroism in the mid-IR range (3µm - 5µm) can reach 80% (when the surface is partially covered with gold) or 65% (when the surface is completely covered with gold) with a single-cycle and single-helical surface. Experimental fabrications of the proposed helical plasmonic surface are implemented with direct 3D laser writing followed by electron beam evaporation deposition of gold. The experimental evaluations of the circular polarization dichroism are in excellent agreement with the simulation. The proposed helical surface structure is of advantages of easy-fabrication, high-dichroism and scalable to other frequencies as a high efficient broadband circular polarizer.

Pixelated metasurfaces integrating both the functions of linear polarization and circular polarization filters on a single platform can achieve full-Stokes polarization detection. At present, the pixelated full-Stokes metasurfaces mainly face the following problems: low transmission, low circular dichroism (CD) of circular polarization filters, and high requirements in fabrication and integration. Herein, we propose high performance ultracompact all-dielectric pixelated full-Stokes metasurfaces in the near-infrared band based on silicon-on-insulator, which is compatible with the available semiconductor industry technologies. Circular polarization filters with high CD are achieved by using simple two-dimensional chiral structures, which can be easily integrated with the linear polarization filters on a single chip. In addition, the dielectric materials have higher transmission than metal materials with intrinsic absorption. We experimentally demonstrated the circular polarization filter with maximum CD up to 70% at a wavelength of 1.6 μm and average transmission efficiency above 80% from 1.48 μm to 1.6 μm. Therefore, our design is highly desirable for many applications, such as target detection, clinical diagnosis, and polarimetric imaging and sensing.

polarization manipulation elements have been the two of the most widely investigated device types because of the essential and indispensable functions of these elements. [5][6][7][8][9] In contrast with the traditional bulky optical lenses, a metalens is a micro/ nanostructured metasurface lens in which the amplitude, phase, and polarization state of the transmitted or reflected electromagnetic waves can be manipulated by the micro/nanostructures at the subwavelength scale based on the effects of surface plasmonic polaritons (SPP) or localized surface plasmonics (LSP), [10][11][12][13][14] Mie resonances, [15] and geometric phase (also known as Pancharatnam-Berry phase, P-B phase), [9,[16][17][18][19][20][21][22][23][24] using which focusing, imaging and/or wavefront manipulation in the transmission or reflection can be achieved. Plasmonic lenses consist of an array of metal plasmonic antennas in which a phase discontinuity related to the geometry and dimension of the metallic antennas appears between the incident electromagnetic wave and the transmitted and/or reflected electromagnetic wave due to the SPP/LSP effects. The ability to generate a spherical wavefront or nondiffracting Bessel beam by an array of gold (Au)_ V-shaped nanoantennas with different geometries and dimensions has been experimentally demonstrated at telecom wavelengths. [13] A dual-polarity metalens consisting of an array of plasmonic dipole antennas on a glass substrate with various orientations has also been experimentally demonstrated, in which a convex or concave lens can be realized with an opposite circular polarized illumination, i.e., either left-handed circular polarization (LCP) or right-handed circular polarization (RCP). [14] Using the similar plasmonic dipoles made of subwavelength metallic nanorods with spatially varying orientations, high-resolution 3D holography can also be achieved. [25] Unlike the plasmonic lens, the all-dielectric metalens based on Mie resonances can also achieve focusing with high efficiency, and a metalens with Si elliptical disks with different dimensions embedded in glass substrate was proposed for this purpose. [15] Recently, the P-B phase has attracted much attention and has been employed in focusing/imaging of the optical metasurface. Unlike the propagation phase, the P-B phase is achieved using azimuth-varied nano/micrograting structures. [26,27] Each nano/microunit (metamolecule) of the metalens is similar to a local half-wave plate (HWP) with different azimuthal angle (θ), so that the circular polarization state of the transmission or reflection is orthogonal to that of the A chiral metalens of circular polarization dichroism (CPD) in the mid-infrared region of 3-5 µm is demonstrated both theoretically and experimentally, in which one of the circularly polarized light beams (either left-handed or righthanded) is transmissively focused at a designed focal length, while the other beam is reflected. The metalens consists of subwavelength helical surface arrays covered by a gold thin film that gives r...

Broadband achromatic metalens imaging is of great interest in various applications, such as integrated imaging and augmented/virtual reality display. Current methods of achromatic metalenses mainly rely on the compensation of a linear phase dispersion implemented with complex nanostructures. Here, we propose and experimentally demonstrate a polarization-insensitive achromatic metalens (PIA-ML) based on computational wavefront coding. In this method, simple circular or square nanopillars are individually coded such that the focal depths at wavelengths at both ends of the achromatic bandwidth overlap at the designed focal plane, which removes the limitation of requiring a linear phase dispersion. An optimized PIA-ML that works in the full optical communication band from 1300 to 1700nm was obtained using a particle swarm optimization algorithm. Experimental results show that both focusing and imaging of the fabricated metalens are consistent with theoretical predictions within the broadband wavelength range, which provides a new methodology for ultra-broadband achromatic imaging with simple-shaped nanostructures.

Compared with intensity imaging, more inherent information of objects can be obtained by polarization and multispectral imaging. Here, a broadband and highly integrated single-chip full Stokes polarization-spectral (FSPS) imaging is demonstrated using all-dielectric spatially multiplexed metalens (SMM) in the wavelength band from 1400 to 1700 nm. The proposed FSPS-SMM is composed of three sets of off-axis sub-metalens simultaneously working for pairs of 0°/90°, 45°/135°linear polarization (LP), and left-handed/right-handed circular polarization (CP), respectively. Experimental results show that the optical resolution of each sub-metalens of the fabricated FSPS-SMM reaches the diffraction limit of the full-aperture metalens although the area of each sub-metalens is only 1/3 of the entire metalens, the averaged polarization extinction ratio of both LP and CP reaches 32.8:1, and the energy efficiency reaches 81.8% at the design wavelength and 60% averagely in the whole 300 nm bandwidth, which breaks the 50% limit of conventional polarizer-based methods. The proposed design provides a new idea for high-efficiency and high-resolution full Stokes polarization-spectral imaging and multichannel information processing.

We proposed and demonstrated a linearly polarized white light emission from an InGaN light-emitting diode with nanograting-integrated fluorescent ceramics. By incorporating a dielectric layer with low refractive index between multilayer nanogratings and a fluorescent ceramic, both high TM transmission (TMT) and high extinction ratio (ER) were effectively achieved across the entire range of white light. An ER higher than 20 dB and a TMT of 60% were obtained experimentally for a GaN/fluorescent-ceramic-integrated white LED with a multilayer grating of 150 nm period. The fluorescent-ceramic-integrated structure showed possibilities of implementing a polarized white LED with high performance.

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